Where this review is coming from: 40-something married couple who wanted a night in Palo Alto.
Why we decided on Hotel Keen: price seemed OK, the simplicity attracted us.
Would we stay there again? Not very likely.

Great for: very tired (so tired that they are dead to the world) solo business travelers and/or folks who need to be downtown.
Not good for: anyone who needs to see the sun, or breath outside air from their hotel room.

The Review:
This hotel is fine/ok, but that's about it.
The desk staff was very nice, attentive and helpful. Upon arrival, they told us that they had upgraded us to a larger room free of charge (which was very nice, naturally). The "larger" room was fairly small (acceptable, but just small in general), so I'm afraid to find out what the smallest rooms are like.
As the other reviews here on Trip Advisor point out, Hotel Keen is a very stark, simple, small boutique hotel with nearly no perks.

...the clean design, and creative use of small space are great and all, but as my wife pointed out, it may be a little bit like what living in a cell might be like. Me, I thought of it as being confined to a cell on a spaceship as you're unaware that you are hurtling through space (kind of like living in the Film "2001"). Why? Well, the fact that there was a single window, which you cannot open, and is made of frosted glass so that it was also almost impossible to tell if it is night or day outside might have had a lot to do with it.
The room was clean, efficient, and generally attractive with its use of curtains instead of doors, and euro-style fixtures, furniture, etc. The bed was comfortable, the TV worked fine.

WHY we wouldn't stay again, or longer than one night; honestly, it is because the impression is that you are basically confined to a cell.
As you walk towards your room down the hallway, you notice there are little blue lights at foot level not unlike the emergency exit lights on a plane. I'm doing what I can to give the best illustration/impression that I can of the place so that you won't be surprised when/if you stay there. Again; I'm not intentionally trying to put the place down, it is fine for what it is, but you should really understand what that is before you stay there.

I think this place would be ideal if you were super, super tired, and all you wanted to do is sleep without knowing if it is daylight or nighttime outside.

There is an acceptable level of "white noise" to the place; the sounds of machines and such muffled through the walls which is typical for any building, but I'm mentioning this so you don't think the place is 100% quiet.

The free 24 hour pod coffee (in the lobby) and "free" continental-style breakfast were nice, but with 3+ bakeries nearby (plus numerous other restaurants all within a couple blocks) you might need to get out of the hotel to not feel like you are still on lock-down in the hotel's confining environment.

SO; if you just need a practical, but small, essentially windowless room to stay in for the purpose of sleeping, and you feel the price is OK, then go for it.
If you want to feel human, however, or if your idea of life is breathing outside air and seeing the sun (from/in the hotel) while staying somewhere, then this won't be the place for you.

On the plus side; seriously close to EVERYTHING downtown.
Parking: we were there for a Saturday night, and had no problem getting a free spot in the lot next door, weekdays would be challenging, and/or at an expense.

Great for what it is. Not so great if you need/want something different than what it offers.